Note: Descriptions are shown in the official language in which they were submitted.
CA 02762520 2016-11-30
WO 2010/135318 PCT/US2010/035243
METHODS FOR FORMING A STRUCTURE
HAVING A LIGHTNING STRIKE PROTECTION
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional Application
No.
61/179,539, filed May 19, 2009, entitled "Methods For Forming A Structure
Having A
Lightning Strike Protection".
FIELD OF THE INVENTION
[0002] This invention relates generally to lightning strike protection for
structures,
and more particularly to methods for automatically applying lightning strike
protection
during the forming of structures such as composite structures.
BACKGROUND OF THE INVENTION
[0003] The extremely high energy of a lightning strike can cause damage to
structures unless adequate protection is provided. Composite structures are
particularly vulnerable due to the relatively low electrical conductivity
compared to
metals. Composite materials are frequently used in aeronautical and aerospace
applications due to their high strength to weight ratio and desirably are
protected
from damage due to lightning strikes.
[0004] Traditionally, composite structures were fabricated using hand layup
with a
conductive layer added manually for lightning strike protection. In order to
minimize
weight, the lightning strike protection is very lightweight and extremely
fragile.
Automated methods such as fiber placement and tape laying machines are
currently
used to automatically fabricate composite structures, however the fragile
lightning
strike protection is still applied manually.
- 1 -
CA 02762520 2011-11-17
WO 2010/135318
PCT/US2010/035243
[0005] Lightning protection for composite structures, includes for example,
U.S.
Patent No. 3,755,713 issued to Paszkowski, which discloses a metal wire mesh
imbedded into a composite structure for lightning strike protection. The metal
mesh,
foil and/or wires are imbedded into the structure using a manual process.
[0006] U.S. Patent No. 6,692,681 issued to Lunde discloses a method and
apparatus for manufacturing composite structures such as an aircraft fuselage.
Following fiber-placement of the outer carbon fiber skin, other layers may be
manually placed. For example, a fabric layer containing metal filaments for
lightning
protection may be manually applied.
[0007] There is a need for further lightning strike protection for
structures, and
more particularly to methods for automatically applying lightning strike
protection
during the forming of structures such as composite structures.
SUMMARY OF THE INVENTION
[0008] In a first aspect, the present invention provides a method for
forming a
structure having lightning strike protection. The method includes receiving at
least
one structural layer, receiving at least one lightning strike protection strip
disposed
on at least one reinforcement layer, the at least one lightning strike
protection strip
comprising a first material, and the at least one reinforcement layer
comprising a
second material different from the first material. The at least one lightning
strike
protection strip disposed on the at least one reinforcement layer is disposed
onto the
at least one structural layer, and the at least one structural layer, the
lightning strike
protection strip, and the reinforcement layer, are formed into the structure.
[0009] In a second aspect, the present invention provides a method for
automatically forming a composite structure having lightning strike protection
using
at least one of a fiber placement apparatus, a tape laying apparatus, and a
similar
automated manufacturing means. The method includes automatically applying at
least one lightning strike protection strip disposed on the at least one
reinforcement
layer onto at least one composite layer using the at least one of the fiber
placement
apparatus, the tape laying apparatus, and the similar automated manufacturing
- 2 -
CA 02762520 2011-11-17
WO 2010/135318
PCT/US2010/035243
means, and at least one of curing and/or melt bonding the at least one
composite
layer, the at least one lightning strike protection strip, and the at least
one
reinforcement layer, into the structure.
[0010] In a third aspect, the present invention provides a lightning strike
protection means for use in automatically forming a structure having lightning
strike
protection. The lightning strike protection means includes a reinforcement
layer, a
lightning strike protection strip disposed on the reinforcement layer, the
lightning
strike protection strip comprising a first material, and the reinforcement
layer
comprising a second material different from the first material, and wherein
the
reinforcement layer and the lightning strike protection strip is operable to
being
automatically applied using at least one of a fiber placement apparatus, a
tape laying
apparatus, and similar automated manufacturing means, and wherein the
reinforcement layer forms a portion of the structure.
[0011] In a fourth aspect, the present invention provides a structure and a
composite structure formed using the above-described methods.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The subject matter which is regarded as the invention is
particularly
pointed out and distinctly claimed in the concluding portion of the
specification. The
invention, however, may best be understood by reference to the following
detailed
description of various embodiments and the accompanying drawings in which:
[0013] FIG. 1 is a perspective view of one embodiment of a composite
structure
having a lightning strike protection means in accordance with one aspect of
the
present invention;
[0014] FIG. 2 is a perspective view of the lightning strike protection
means
disposed on a release or backing sheet;
- 3 -
CA 02762520 2011-11-17
WO 2010/135318
PCT/US2010/035243
[0015] FIG. 3 is a schematic side view of one embodiment of a tape laying
apparatus for automatically forming a composite structure with the lightning
strike
protection means of FIG. 1;
[0016] FIG. 4 is a perspective view of another embodiment of a composite
structure in accordance with another aspect of the present invention having
lightning
strike protection means in which a portion of adjacent lightning strike
protection strips
overlap;
[0017] FIG. 5 is a perspective view of another embodiment of a composite
structure in accordance with another aspect of the present invention having
lightning
strike protection means in which portions of adjacent lightning strike
protection are
spaced apart to define a gap;
[0018] FIG. 6 is a flowchart of one embodiment of a method for forming a
structure having lightning strike protection in accordance with one aspect of
the
present invention; and
[0019] FIG. 7 is a flowchart of another embodiment of a method for
automatically
forming a composite structure having lightning strike protection using at
least one of
a fiber placement apparatus, a tape laying apparatus, and a similar automated
manufacturing means in accordance with one aspect of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The present invention is directed to lightning strike protection of
structures
such as composite structures and especially for fiber placed or tape laid
composite
structures. Aeronautical and aerospace structures are especially applicable
since
the high performance structures (such as but not limited to helicopters,
airplanes,
UAVs and missiles) are currently fabricated using fiber placement, tape laying
technologies and other automated fabrication means.
- 4 -
CA 02762520 2011-11-17
WO 2010/135318
PCT/US2010/035243
[0021] As used herein, the following terms are defined as follows:
[0022] Lightning strike protection strip: Any layer or layers of
electrically
conductive materials applied to any structure for the purpose of dissipating
the
electrical energy of a lightning strike. Such layer or layers may consist of
metal foil,
expanded foil, wire mesh, wires, conductive fibers, nanotubes, conductive
plastics,
conductive fillers in a matrix, or any other suitable material or
configuration.
[0023] Tape laying: A fabrication process in which wide prepreg tape is
laid side
by side or overlapped to form a relatively flat structure.
[0024] Automated fiber placement: Automated Fiber Placement (AFP) is
traditionally differentiated from tape laying by considering the process to
utilize a
plethora of narrow, individual slit tapes or tows to make up a given total
prepreg
band width. Complex geometries that demand complex fiber placement are
typically
approached by the industry with multiple 0.125 inch ¨ 0.250 inch tows or
tapes.
[0025] Thermoplastic: A plastic material that is capable of being
repeatedly
softened by application of heat and repeatedly hardened by cooling. Softening
and
hardening are reversible for a thermoplastic.
[0026] Thermoset: A plastic material that is capable of being cured by heat
or
catalyst into an infusible and insoluble material. Once cured, a thermoset
cannot be
returned to the uncured state. Thus, hardening is irreversible for a
thermoset.
[0027] Aspects of the present invention are directed to methods for
applying
lightning strike protection to any surface including, but not limited to,
composite
structures. For example, a composite structure may be formed from a plurality
of
layers. The composite may comprise a matrix material such as a binder or
resin,
and comprise a reinforcing material such as a plurality of fibers or other
structures
formed from graphite, fiberglass, aramid, or other materials. The matrix
material
such as a thermoplastic or thermoset material surrounds and supports the
reinforcing material by maintaining their relative positions. The layers may
be in the
form of a tape having a large width relative to the thickness of the tape. For
- 5 -
CA 02762520 2016-11-30
WO 2010/135318 PCT/US2010/035243
example, the composite tape may have a width of about 1 inch to about 12
inches,
and preferably about 1 inch for complex structures inches, and about 6 inches
or
about 12 inches for generally flat surfaces of structures.
[0028] The technique of the present invention employs conventional
automated
fiber placement equipment, tape laying equipment, or other equipment or
apparatus
to place the lightning strike protection in the same manner as the other
layers in the
underlying composite structure. In so doing, a manufacturer may be able to
extend
the use of existing equipment, improve the final product, and improve
manufacturing
efficiency.
[0029] FIG. 1 is a perspective view of one embodiment of a structure 20
such as
a composite structure in accordance with one aspect of the present invention.
Structure 20 includes a lightning strike protection means 30 comprising a
lightning
strike protection strip 50 disposed on at least one reinforcement layer 40
which is
disposed on at least one structural layer 60.
[0030] FIG. 2 is a perspective view of one embodiment of lightning strike
protection means 30 disposed on a release or backing sheet 70 prior to
lightning
strike protection means 30 being removed from backing sheet 70 and disposed on
structural layers 60 (FIG. 1) such as being automatically deposited.
[0031] For example, with reference to FIG. 3, one aspect of the present
invention
may be implemented on a fully automated apparatus 10 to laminate various
structural articles with a layer of resin impregnated fiber tape. The
apparatus may
remove a releasable backing layer from the tape or structural layers being
employed,
then deposit the unbacked tape on the surface of the structural article, and
finally
sever the end of the tape being deposited. An automated cut and restart
procedure
may be employed to increase tape throughput. Such a fully automated apparatus
is
described in U.S. Patent No. 7,063,118 issued to Hauber et al.
It will be appreciated by
those skilled in the art that the technique of the present invention may be
implemented on other suitable automated fiber placement equipment, automated
tape laying equipment, and similar automated placement means.
- 6 -
CA 02762520 2011-11-17
WO 2010/135318 PCT/US2010/035243
[0032] With reference again to FIGS. 1 and 2, in accordance with one aspect
of
the present invention, the reinforcement layer is applied to the lightning
strike
protection strip to support the lightning strike protection strip during the
fiber
placement, tape laying or other suitable process. The reinforcement layer may
be
unidirectional, cross-ply, woven, non-woven or other geometries that has
sufficient
strength/stiffness to ensure that tensile stresses are borne by the
reinforcing layer to
minimize the stresses applied to the relatively fragile lightning strike
protection. The
reinforcement layer may also comprise any suitable material such as graphite,
fiberglass, aramid, linear polyolefin, ceramic, metal, etc. in any suitable
length so
long as its addition results in an increased tensile strength and/or stiffness
of the
lightning strike protection strip. For example, the reinforcement layer may
have a
width of about 1 inch to about 12 inches, and preferably about 1 inch for
complex
structures inches, and about 6 inches or about 12 inches for generally flat
surfaces
of structures. The lightning strike protection strip may have the same width
as the
reinforcement layer or may be wider or narrower as described below for forming
gaps between adjacent lightning strike protection strips or overlapping of the
lightning strike protection strips.
[0033] For example, the lightning strike protection strip may comprise a
first
material such as a metal and the reinforcement layer may comprise a second
material such as a composite material comprising fibers and a matrix. The
structure
or structural layer may comprise a third material and the second material of
the
reinforcement layer may be the same as the third material. For example, the
reinforcement layer may be the same material as the underlying structure,
e.g., a
composite material.
[0034] The reinforcement layer may be bonded or unbonded to the lightning
strike
protection prior to fiber placement. Preferably, but not necessarily, the
reinforcement
layer is bonded to the lightning strike protection using the same adhesive as
is used
for the remainder of the structure. For example, a thermosetting epoxy
adhesive
may be used in the case of an epoxy composite laminate and a thermoplastic
adhesive may be used in the case of a thermoplastic composite laminate, etc.
This
may ensure a cohesive bond between the various layers of the structure.
- 7 -
CA 02762520 2011-11-17
WO 2010/135318
PCT/US2010/035243
[0035] In one embodiment, a lightning strike protection strip may have a
thickness
of about 0.0035 inch, and the reinforcement layer may have thickness of about
0.005
inch. For example, a lightning strike protection strip may comprise an
expanded
copper metal foil 0.0035 inch thick, and the reinforcement layer may be a
0.005 inch
thick graphite fiber reinforced PEEK composite tape. From the present
description, it
will be appreciated that other materials and thicknesses may be suitably
employed.
[0036] Some aspects of the present invention may solve the problem of
forming a
conductive pathway to dissipate the energy of a lightning strike in a
structure, for
example, by placing the edges of the strips of lightning strike material
adjacent to
each other to optimize electrical conduction between the adjacent layers.
[0037] Such placement of adjacent strips may include overlapping lightning
strike
protection strip to improve electrical conduction. For example, as shown in
FIG. 4, a
structure 120 may include a portion of a lightning strike protection strip 150
which is
wider than a reinforcement layer 140 such that lightning strike protection
strip 150
overlaps that of a portion of an adjacent lightning strike protection strip
150 to
improve electrical conduction between adjacent strips. Such conduction may be
further optimized by the selective application of other materials such as, but
not
limited to, conductive carbon filaments, nanotubes, conductive fillers or any
other
suitable means.
[0038] Such placement of adjacent strips may include a controlled gap to
dissipate energy across the structure in selected directions. For example, as
shown
in FIG. 5, a structure 220 may include a portion of a lightning strike
protection strip
250 may be spaced-apart from a portion of an adjacent lightning strike
protection
strip 250 such that a gap is formed therebetween to dissipate energy across
the
structure. In addition, a controlled overlapping and spacing apart of adjacent
strip
may be employed to tailor the conduction and dissipation of energy across the
structure.
[0039] A further aspect of the present invention may include providing a
smooth
surface finish to the lightning strike protection. As the lightning strike
protection is
disposed on or near the outer surface of the structure, it may be desirably
that the
- 8 -
CA 02762520 2011-11-17
WO 2010/135318 PCT/US2010/035243
lightning strike protection have a smooth surface finish. For example, the
lightning
strike protection strip may be embedded into a matrix material, a surface veil
applied
over the lightning strike protection, and the lightning strike protection may
be
traversed with a subsequent smoothing pass or passes with the fiber placement,
tape placement or other manufacturing equipment to improve surface finish
alone or
in combination with other processes.
[0040] In another example, a support layer may be applied over the
lightning
strike protection strip to provide a sacrificial surfacing layer without
disturbing the
lightning strike protection, to provide electrical continuity, and to provide
improved
surface finish and the ability for subsequent machining steps to provide a
smooth
surface finish and accurate outside dimensions. Such external sacrificial
layer may
be applied as one, two or more layers of different materials or the same
material with
different colors so that subsequent machining steps will visibly show when one
layer
has been breached and before the lightning strike protection has been damaged.
[0041] Fiber placement and tape laying machinery or the like are intended
to
place relatively strong composite fibers and not designed to solely place
relatively
fragile lightning strike protection to the structure. The present invention
solves the
problem of damage to the lightning strike means during automated manufacture
by
adding a reinforcement layer to the lightning strike protection to support the
lightning
strike protection during fiber placement, tape laying or other suitable
process. By
employing a reinforcement layer, the fragile lightning strike protection may
be readily
applied to a structure whether simple or complex geometry using the fiber
placement
and tape laying machinery or the like.
[0042] FIG. 6 is a flowchart of one embodiment of a method 300 for forming
a
structure having lightning strike protection in accordance with one aspect of
the
present invention. The method may include at 310, receiving at least one
structural
layer, and at 320, receiving at least one lightning strike protection strip
disposed on
at least one reinforcement layer. The at least one lightning strike protection
strip
comprises a first material, and the at least one reinforcement layer
comprising a
second material different from the first material. At 330, the at least one
lightning
strike protection strip disposed on the at least one reinforcement layer is
applied onto
- 9 -
CA 02762520 2011-11-17
WO 2010/135318
PCT/US2010/035243
the at least one structural layer, and at 340, the at least one structural
layer, the
lightning strike protection strip, and the reinforcement layer, are formed
into the
structure.
[0043] FIG. 7 is a flowchart of another embodiment of a method 400 for
automatically forming a composite structure having lightning strike protection
using
at least one of a fiber placement apparatus, a tape laying apparatus, and a
similar
automated manufacturing means in accordance with one aspect of the present
invention. The method may include at 410, automatically receiving at least one
composite layer, and 420, automatically applying the at least one composite
layer
using at least one of the fiber placement apparatus, tape laying apparatus,
and
similar automated manufacturing means. At 430, at least one lightning strike
protection strip disposed on at least one reinforcement layer is automatically
received. The at least one lightning strike protection strip comprises a first
material,
and the at least one reinforcement layer comprising a second material
different from
the first material. At 440, the at least one lightning strike protection strip
disposed on
the at least one reinforcement layer is automatically disposed onto the at
least one
composite layer using the at least one of the fiber placement apparatus, the
tape
laying apparatus, and the similar automated manufacturing means. At 450, the
at
least one composite layer, the at least one lightning strike protection strip,
and the at
least one reinforcement layer, are at least one of cured and melt bonded into
the
structure.
[0044] Although the invention has been particularly shown and described
with
reference to certain preferred embodiments, it will be readily appreciated by
those of
ordinary skill in the art that various changes and modifications may be made
therein,
without departing from the spirit and scope of the invention.
* * * * *
- 10 -
